Libretro

RetroArch is a multi-system emulator for Linux, Windows, Mac OS X and *BSD. It is formerly known as SSNES.

Its design and background is quite different than most other emulators as RetroArch does not implement an emulation core itself. RetroArch talks to libretro, a generic emulator core API. This means that RetroArch is core agnostic, and it does not care which emulator core is running.